Analysis of reflectance and fluorescence spectra for atypical features: Fluorescence in the yellow-green

An experiment designed to search for remotely detectable, identifying features of anthropogenic contaminants by remote sensing of vegetation is described. Reflectance and fluorescence measurements are made from single leaves, still attached to the plant. In order to maximize the opportunity for detection and identification of possibly subtle spectra features, all optical measurements are made under controlled conditions. Reflectance is measured using diffuse illumination and a well-defined illumination and viewing geometry over a wide range of wavelengths (0.35-2.5 μm). Fluorescence spectra are measured from live leaves at over 30 excitation wavelengths. Analysis procedures are designed to facilitate sorting through large amounts of data and allow interactive manipulation of the spectral data sets. Reflectance of single leaves from soybean plants subjected to water stress differed little from reflectance of the leaves from control plants. (This may not be indicative of canopy reflectance.) Blue and red fluorescence was somewhat greater for the water stressed plants. Unusual fluorescence features in the yellow-green part of the spectrum were also found in both control and the stressed plants. These features were exceptionally sensitive to stress.